Recently, there is developed an intelligent resin molding which measures temperature, pressure, flow speed and the like of a molten resin in a cavity of an injection mold and controls molding conditions. Further, there is suggested an ejector pin including an optical fiber, installed in a hollow portion of a metal sleeve, for measurement of a temperature of the molten resin in the cavity (see, e.g., Japanese Patent Application Publication No. 2008-14686).
Hereinafter, a conventional ejector pin in which an optical fiber is installed in a metal sleeve will be described with reference to FIGS. 5A and 5B.
FIG. 5A is a cross sectional view taken along a longitudinal direction (axial direction) of an ejector pin (except an optical fiber Fs), and FIG. 5B is a cross sectional view taken along line VB-VB of FIG. 5A.
The ejector pin includes a metal sleeve 11 having a hollow portion extending in the axial direction, and a spacer 12 made of stainless steel is fixed in a part of the hollow portion has a larger inner diameter. An optical fiber Fs of a single line (single strand) is inserted into the hollow portion and fixed to the spacer 12 by heat resistant resin (heat resistant adhesive) 13 such as epoxy resin or the like.
As shown in FIG. 5A, a leading end of the metal sleeve 11 is exposed to a cavity 15 of the injection mold, and the rear end of the metal sleeve 11 is coupled (connected) to a light receiving portion 14. When molten resin is injected into the cavity 15, infrared rays are emitted from the molten resin. The infrared rays are transmitted to the light receiving portion 14 through the optical fiber Fs, as indicated by an arrow L1. The infrared rays transmitted to the light receiving portion 14 are converted into electric signals and used for measuring a temperature of the molten resin.
The ejector pin shown in FIGS. 5A and 5B uses a single line optical fiber. Therefore, in order to measure a flow speed of the molten resin in the cavity 13, two optical fibers for light emission and light reception are required. Further, when the optical fibers for light emission and light reception are each made of a single line, the light emitting/receiving amount transmitted therethrough is small and, thus, it is difficult to transmit a sufficient amount of light which is required to measure the flow speed of the molten resin.
In order to increase the light emitting/receiving amount, a so-called bundle fiber, including a plurality of lines of optical fibers tied together, needs to be used.
Meanwhile, the bundle fiber is formed by binding several optical fibers, so that the surface (outer peripheral surface) thereof is uneven and has an incomplete circular cross section. Therefore, when the bundle fiber is fixed to the hollow portion of the metal sleeve 11 by the heat resistant resin 13 as shown in FIGS. 5A and 5B, a clearance is generated between the bundle fiber and the spacer 12, which makes it difficult to obtain an adhesive (fixing) strength that ensures endurance against the resin pressure in the cavity cannot be obtained.
Accordingly, the present inventor has manufactured, as a trial, a pin having a bundle fiber shown in FIGS. 6A and 6B.
FIG. 6A is a cross sectional view taken along a longitudinal direction (axial direction) of the pin having a bundle fiber (except the bundle fiber Fb), and FIG. 6B is a cross sectional view taken along line VIB-VIB of FIG. 6A.
The pin having the bundle fiber shown in FIGS. 6A and 6B includes an outer metal sleeve (pin sleeve) 21, a metal bundle sleeve 22, and the bundle fiber Fb. The bundle sleeve 22 is fixed to an inner surface of the outer sleeve 21 by a heat resistant resin such as an epoxy resin or the like. Further, the bundle fiber Fb is inserted into the hollow portion of the sleeve 22. The pin having the bundle fiber has a leading end exposed to the cavity 25 and a rear end connected (coupled) to the light emitting/receiving portion 24.
Here, the end of the pin having the bundle fiber which faces the cavity 25 is referred to as “leading end,” and the other end (the end facing the light emitting/receiving portion 24) is referred to as “rear end.” Further, a portion close to the leading end of the pin having the bundle fiber is referred to as “leading end portion” and a portion close to the rear end is referred to as “rear end portion.” This is the same in the following description.
The bundle fiber Fb is manufactured by binding a plurality of optical fibers into a bundle by thermal pressing without using an adhesive, and thus has a high heat resistance.
The bundle fiber Fb is maintained by caulking (firmly tightening) the leading end portion of the bundle sleeve 22 in a cone shape. A substantially cone-shaped caulked portion 221 has a tapered shape that becomes gradually narrower toward the leading end.
The cross sectional shape of the bundle fiber Fb is illustrated as a complete circle, for convenience. However, it is generally not a complete circle and has an uneven surface (outer peripheral surface).
When the leading end portion of the bundle sleeve 22 is caulked, a gap is generated between the caulked portion 221 and the inner surface of the hollow portion of the outer sleeve 21. The gap is filled by the heat resistant resin (heat resistant adhesive) 23 such as epoxy resin or the like. The inclined angle of the caulked portion 221 is set to about 10°.
The light generated from the light emitting portion 241 of the light emitting/receiving portion 24 is transmitted to the cavity 25 through a part of the optical fibers of the bundle fiber Fb and irradiates the molten resin in the cavity 25. The light reflected from the molten resin is transmitted to the light receiving portion 242 of the light emitting/receiving portion 24 through the other optical fibers of the bundle fiber Fb and is converted into an electrical signal. The flow speed of the molten resin in the cavity 25 is measured (calculated) by the electrical signal. Arrows L2 indicate light directed from the light emitting portion 241 toward the bundle fiber Fb and light reflected from the molten resin in the cavity 25 and directed toward the light receiving portion 242 through the bundle fiber Fb.
Since the leading end of the pin having the bundle fiber shown in FIGS. 6A and 6B is exposed to the cavity 25, the heat resistant resin 23 is softened by the heat of the molten resin in the cavity 25 and depressed by the molten resin pressure. Further, the heat resistant resin 23 may be eroded by the gas generated by the molten resin.